This project, as well as project number ZO1-CP-04842-05-LVC, studies the biochemical and biophysical properties of nucleic acids of mammalian oncornaviruses. A summary of our major findings for this fiscal year are as follows: 1. Poly(A), poly(C) and poly(G)-rich sequences or tracts have been detected. 2. Poly(U)-rich sequences have not been detected. 3. Four classes of viral RNA subunits have been identified according to their polynucleotide compositions.